Single-use syringe

ABSTRACT

An operable single-use syringe includes a barrel having an inside surface defining a chamber for retaining fluid and an open proximal end. A plunger rod having an elongate body portion and a stopper at its distal end slidably positioned in fluid-tight engagement in the barrel. A locking element is positioned in the barrel between the plunger rod and the inside surface of the barrel. The locking element has a base and two leg members projecting therefrom that are positioned in longitudinal grooves in the plunger rod. The locking element only moves distally in the barrel and prevents re-use of the syringe after its contents have been discharged.

BACKGROUND OF THE INVENTION

The present invention relates to syringe assemblies and particularly tosyringe assemblies having an automatic disabling mechanism.

Throughout the world the multiple use of hypodermic syringe productswhich are intended for single-use only, is instrumental in drug abuseand in the transfer of contagious diseases. Intravenous drug users whoroutinely share and re-use syringes are a high-risk group with respectto the AIDS virus. Also, the effects of multiple use are a major concernin some countries where repeated use of syringe products during massimmunization programs may be responsible for the spread of manydiseases. Re-use of single-use hypodermic syringe assemblies is alsoinstrumental in the spread of drug abuse even in the absence ofinfection or disease.

Many attempts have been made to remedy this problem. Most notable areearly contributions which relies on a specific act to destroy thesyringe after use either by using a destructive device or providingsyringe assembly with frangible zones so that the syringe could berendered inoperable by the application of force. Other attempts involvethe inclusion of structure which would allow the destruction ordefeating of the syringe function by a conscious act of the syringeuser. Although many of these devices work quite well, they require thespecific intent of the user followed by the actual act to destroy orrender the syringe inoperable. These devices are not effective with auser having the specific intent to re-use the hypodermic syringe.Accordingly, there was a need for a single-use hypodermic syringe whichafter use will become inoperable or incapable of further useautomatically without any additional act on the part of the user. Theautomatic function is much harder to provide because the means forrendering the syringe inoperable must not prevent its filling or useunder normal conditions.

Single-use syringes which automatically disable after injection aretaught in the art. Some of these syringes contain a locking elementpositioned in the syringe barrel between the plunger rod and the insidesurface of the barrel. In use, the syringe allows the user to draw apre-selected amount of medication into the chamber of the barrel anddeliver this medication, as through injection, into the patient. Anyattempt to withdraw the plunger to use the syringe a second time willcause the locking element to embed itself into the inside surface of thebarrel to prevent proximal motion of the plunger rod.

Many times a traditional multi-use syringe and needle assembly are usedto reconstitute lyophilized medication. The steps for reconstitutioninclude withdrawing sterile water from a stoppered vial or glass ampouleinto the syringe barrel and then delivering this water into a stopperedvial or glass ampoule containing the lyophilized medication. Thereconstituted medication is then drawn into a single-use syringe fordelivery to the patient. Single-use syringes designed specifically forreconstitution and which cannot be used for injecting medication into apatient are not presently available.

Further, mass immunization programs usually take place in developing,countries where resources are limited. Accordingly, sometimes withlimited resources a number of people immunized can be increased if thecost of the medication and/or the syringe is reduced. It is notdesirable to reduce the cost of the single-use syringe by compromisingits features since those intent on re-using syringes can be veryaggressive and resourceful in their attempts to disable the safetyfeatures.

Accordingly, there is always a needle for single-use syringes which aremore cost-effective and more resistant to improper re-use. Further,there is a need for a single-use syringe which is only capable ofreconstitution of a dried or lyophilized drug substances and not capableof injection into the human body.

SUMMARY OF THE INVENTION

An operable single-use syringe comprises a barrel having an insidesurface defining a chamber for retaining fluid, an open proximal end anda distal end having a distal wall with a tip extending distallytherefrom having a passageway therethrough in fluid communication withthe chamber. A plunger rod includes an elongate body portion defining alongitudinal axis, a proximal end and a distal end, a stopper at thedistal end is slidably positioned in fluid-tight engagement in thebarrel. The stopper may be integrally formed as part of the plunger rodor be a separate base made of the same material as the plunger rod oranother material such as a thermoplastic elastomer, natural rubber,synthetic rubber and the like. The body portion of the plunger rodextends outwardly from the open proximal end of the barrel and includesa compress at its distal end to facilitate movement of the plunger rod.The body portion includes two parallel longitudinal slots wherein atleast one of the slots includes a plurality of axially-spaceddiscontinuities, the discontinuities may take various shapes such as asaw tooth or ratchet-like structure. A locking element is positioned inthe barrel between the elongate body portion of the plunger rod and theinside surface of the barrel. The locking element has a proximal end, adistal end, a base and two leg segments in substantially parallelrelationship extending from the base into each of the longitudinalslots. The locking element has one or more outwardly and distal endbarbs and one or more outwardly and distally directed proximal endbarbs. The barbs are for engaging the inside surface of the barrel toprevent proximal motion of the locking element with respect to thebarrel. The legs include at least one deflectable, proximallypositioned, resisting element for engaging the discontinuities on theplunger rod for moving the locking element in a distal direction alongthe inside surface of the barrel when the plunger rod is advanced in anadditional direction and allowing proximal motion of the plunger rodwith respect to locking element for filling the chamber.

The plunger rod may also include a proximal end barrier at its proximalend for establishing the most proximal position of the locking elementon the plunger rod. The proximal end barrier may be configured to blockaccess to the locking element through the open end of the barrel. Theplunger rod may also include a distal end barrier at its distal end forestablishing the distal-most position of the locking element on theplunger rod.

The single-use syringe may include a deflectable proximal resistingelement on each leg member of the locking element. Each of the lockingslots may include a plurality of axially-spaced discontinuities. Thedeflectable proximal resisting elements may face outwardly away fromeach other to engage the plurality of spaced discontinuities in eachslot which face inwardly toward each other.

The single-use syringe may be configured so that the length of thelocking element is less than 20% of the distance between the proximalend barrier and the distal end barrier.

The distal end of the locking element may include a distally directedcutting edge capable of cutting into and through the stopper ifexcessive proximally direct force is applied to the plunger rod toovercome the locking element and remove the plunger rod from the barrel.

The single-use syringe of the present invention may also include aneedle assembly including a cannula having a proximal end, a distal endand a lumen therethrough. A hub having an open proximal end including acavity therein, a distal end joined to the proximal end of the cannulaso that the lumen is in fluid communication with the cavity. The tip ofthe barrel engages the hub so that the lumen of the cannula is in fluidcommunication with the chamber of the barrel.

The single-use syringe may also include an elongate cannula made ofthermoplastic material. The cannula includes an inside surface, aproximal end, a distal end and a lumen therethrough defining alongitudinal axis. The outside surface of the cannula at its proximalend has at least one discontinuity. The distal end of the cannulaincludes a stopper-piercing tip. The barrel is made of thermoplasticmaterial wherein the tip of the barrel is formed in intimate contactaround the proximal end of the cannula engaging the at least onediscontinuity so that the lumen is in fluid communication with thechamber.

The tip of the cannula may include a closed distal end and at least oneside aperture in fluid communication with the lumen. Alternatively, thetip of the cannula may include a planar surface at an obtuse angle withrespect to the longitudinal axis of the cannula.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of one embodiment of thesingle-use syringe of the present invention.

FIG. 2 is a perspective view of the plunger rod of the syringe of FIG. 1as viewed from the proximal end.

FIG. 2A is a partially cross-sectioned view of the plunger rod of FIG. 2taken along its longitudinal axis.

FIG. 3 is a perspective view of the plunger rod as viewed from thedistal end.

FIG. 3A is a partially cross-sectioned view of the plunger rod of FIG. 3taken along its longitudinal axis.

FIG. 4 is a perspective view of the locking element viewed from theproximal end.

FIG. 5 is a perspective view of the locking element viewed from thedistal end.

FIG. 6 is a perspective view of the single-use syringe before use.

FIG. 7 is an enlarged partially cross-sectioned side-elevation view ofthe single-use syringe of FIG. 6.

FIG. 8 is a partially cross-sectioned side-elevation view of thesingle-use syringe after liquid has been drawn into the barrel chamber.

FIG. 9 is an enlarged partial side-elevation view of the syringeassembly of FIG. 8.

FIG. 10 is a partially cross-sectioned side-elevation view of thesingle-use syringe after discharge of liquid from the chamber of thebarrel.

FIG. 11 is an enlarged partial side-elevation view of the syringeassembly of FIG. 10.

FIG. 12 is an enlarged partially cross-sectioned view, similar to FIG.11, showing the locking element cutting through the stopper.

FIG. 13 is an enlarged cross-sectional view of the syringe of FIG. 6taken along line 13-13.

FIG. 14 is a partially cross-sectioned side-elevation view illustratingthe single-use syringe being used to remove sterile liquid from astoppered vial.

FIG. 15 is a partially cross-sectioned side-elevation view showing thesingle-use syringe being used to withdraw sterile liquid from a glassampoule.

FIG. 16 is a side-elevational cross-sectional view of the distal end ofthe single-use syringe barrel showing an alternative cannula tip.

FIGS. 17-19 illustrate a removable needle assembly for use with thesingle-use syringe.

DETAILED DESCRIPTION OF THE INVENTION

There is shown in the drawings and will be described in detail hereinpreferred embodiments of the invention with the understanding that thepresent disclosure is to be considered exemplary of the principles ofthe invention and is not intended to limit the invention to theembodiments illustrated. The scope of the invention will be measured bythe appended claims and their equivalents.

For the purpose of the description of the present invention, the term“distal end” is intended to refer to the end furthest from the personholding the syringe, whereas the term “proximal end” is intended torefer to the end closest to the holder of the syringe.

An operable single-use syringe comprises a barrel 21 having an insidesurface 22 defining a chamber 23 for retaining fluid, an open proximalend 25 and a distal end 26 having a distal wall 27 with a tip 28extending distally therefrom having a passageway 29 therethrough influid communication with the chamber.

A plunger rod 31 includes an elongate body portion 32 defining alongitudinal axis 34, a proximal end 35 and a distal end 37. A stopper38 at the distal end of the plunger rod is slidably positioned influid-tight engagement in the barrel. The stopper may be a separateelement connected to the body portion of the plunger rod. The separatestopper may be made of thermoplastic materials, thermoplasticelastomers, natural rubber, synthetic rubber and combinations thereof.The stopper in this embodiment is integrally formed with the elongatebody portion and it is made of thermoplastic material such aspolyethylene. The body portion of the plunger rod extends outwardly fromthe open proximal end of the barrel to facilitate moving the stopper inthe barrel. The body portion includes two parallel longitudinal slots 39and 40. At least one of the slots includes a plurality of axially-spaceddiscontinuities such as ratchet-like teeth 41 in slot 39. In thisembodiment, longitudinal slot 40 also includes axially-spaceddiscontinuities in the form of a ratchet-like teeth 42. The teethinclude distally-facing surfaces 44 and inclined surfaces 45. As will beexplained hereinafter, the axially-spaced discontinuities can take awide variety of shapes and forms all falling within the purview of thepresent invention with the ratchet-like teeth being merelyrepresentative of these various possibilities.

A locking element 51 is positioned in the barrel between the elongatebody portion of the plunger rod and the inside surface of the barrel.The locking element includes a proximal end 52, a distal end 53, a base55 and leg members 56 and 57 in substantially parallel relationshipextending from the base into each of the longitudinal slots in theplunger rod. A locking element has at least one outwardly and distallydirected distal end barb, and in this embodiment there are two distalend barbs 58 and 59 for engaging the inside surface of the barrel toprevent proximal motion of the locking element with respect to thebarrel. The locking element also includes at least one outwardly anddistally directed proximal end barb, and in this embodiment includesproximal end barbs 62 and 63 also for engaging the inside surface of thebarrel to prevent proximal motion of the locking element with respect tothe barrel. There should be at least one deflectable resisting elementextending from one of the leg members. In this embodiment there are twodeflectable resisting elements 64 and 65 for engaging the ratchet-liketeeth on the plunger rod for moving the locking element in a distaldirection along the inside surface of the barrel when the plunger rod isadvanced in a distal direction and allowing proximal motion of theplunger rod with respect to the locking element when filling thechamber. In this embodiment, axially-spaced discontinuities in the formof ratchet-like teeth 41 and 42 face each other while deflectableresisting elements 64 and 65 face outwardly away from each other forengaging the discontinuities. Plunger rod 31 in this embodiment issymmetric along its longitudinal axis having longitudinal slots withdiscontinuities on two sides. This symmetric configuration is believedto improve manufacturability by reducing the angle the plunger must berotated to align with a locking element positioned for insertion in thelongitudinal slots of the plunger rod. With this two-sided configurationthe maximum angle a plunger rod must be rotated to accept a lockingelement is 90° versus 180° for a non-symmetrical plunger rod having onlythe two longitudinal slots.

In this embodiment the plunger rod includes a distal end barrier 46 atthe distal end of the body portion for establishing the distal-mostposition of the locking element on the plunger rod. In this embodiment,the stopper and the distal end barrier are integrally formed. Thisembodiment also includes a proximal end barrier 47 at the proximal endof the plunger rod for establishing the most proximal position of thelocking element on the plunger rod. The proximal end barrier ispreferably large enough to block a substantial portion of the bore ofthe barrel for blocking access to the locking element through the openproximal end of the barrel. This structural feature will frustrateattempts to use small tools to defeat the locking element and improperlyre-use the syringe. A proximal end barrier that is large enough to blockdirect visual contact with the locking element through the open proximalend of the barrel should be large enough to block access to the lockingelement. Also, the channel-shaped locking element is supported andshielded from tampering by relatively large sidewalls 49 on the plungerrod. Further, the substantial structure of the plunger rod surroundingthe locking element supports the locking element and helps it resistattempts to overcome the locking element by improperly twisting theplunger rod because rotation of the plunger rod drives the distal andproximal end barbs into the inside surface of the barrel furtherenhancing the grip of the locking element to the barrel. Also,connection 48 holding thumb press 50 on proximal end of elongate bodyportion 32 can be made frangible by structure and/or material so thatexcessive twisting or tension forces applied to the thumb press willcause it to disconnect from the remainder of the plunger rod to providefurther resistance to improper tampering. These structural andfunctional improvements are important aspects of the present invention.

As best seen in FIGS. 7 and 8 the maximum stroke of the plunger rod, andtherefore the maximum volume the syringe can deliver, is a function ofdistance A between distal end barrier 46 and proximal end barrier 47minus the axial length B of the locking element. The channel-shapedconfiguration of locking element 51 and the support provided by thestructure surrounding the longitudinal slots in the plunger rod allowlocking element length B to be less than some other prior art lockingelements while still being strong enough to prevent re-use. Accordingly,all things being equal, short locking element 51 will allow more volumeto be delivered from the syringe. The locking element and plunger rod ofthe present invention has been configured to fit an available 5 mlsyringe barrel and still allow the delivery of a full 5 ml dose. Someprior art devices yield less than half the volume that the syringebarrel is capable of delivering in a non-single-use configuration. Usingthe structure of the present invention results in a more cost-effectivesingle-use syringe structure therefore making more syringes availablefor mass immunization in a fixed budget program. It is preferred thataxial length B of the locking element be less than 20% of the distance Abetween the distal end barrier and the proximal end barrier. As shown inFIGS. 1, 6 and 7, the locking element is positioned in its distal-mostposition allowing for the maximum delivery volume. However, the deliveryvolume for the syringe can be reduced by initially positioning thelocking element distally from the proximal barrier.

As will be explained in more detail hereinafter, the single-use syringeof the present invention can be used in conjunction with a removableneedle assembly, a permanently attached needle for injection or aplastic cannula suitable for reconstitution and not for human injection.In this embodiment the single-use syringe is illustrated with athermoplastic cannula to function as a single-use reconstitution syringeassembly. In particular, cannula 71 preferably made of thermoplasticmaterial, includes an outside surface 72, a proximal end 73, a distalend 75 and a lumen 77 therethrough defining a longitudinal axis 78.Outside surface 72 at the proximal end of the cannula includes at leastone discontinuity. In this embodiment the at least one discontinuityincludes annular grooves 81 and annular projections 82.

The distal end of the cannula includes piercing tip 83. The piercing tipis much less sharp than the tip of a metal hypodermic needle, but stillsharp enough to pierce the elastomeric stopper of a medication vial. Thecannula at the distal end is much larger than a hypodermic needleintended for injection. In this embodiment, the distal end of thecannula has an outside diameter of at least 2 mm (0.08 inch). Thecombination of the large diameter distal end of the cannula and therelatively blunt piercing tip results in a cannula that is unsuitablefor injection and much less likely to cause accidental skin piercingwhich could result in injury or transfer of disease. The term “piercingtip” as used herein is intended to encompass the tips of larger thaninjection needle diameter being configured to piece elastomeric septumsof injection vials and not human skin under normal use. The cannulaincludes the proximal portion having a diameter larger than the diameterof the distal portion. The diameter of the proximal end is equal orgreater than about 2.5 mm (0.1 inch). The increased proximal portiondiameter substantially strengthens the cannula when bending forces areapplied without, as will be explained hereinafter, interfering with theability to function properly.

In this embodiment, the distal end of the cannula at the piercing tip isclosed and includes at least one side aperture 84 in fluid communicationwith lumen 77.

Piercing tips within the purview of the present invention can includeother configurations. FIG. 16 illustrates an alternative embodimentwherein cannula 171 includes an outside surface 172, a proximal end 173,a distal end 175 and a lumen 177 therethrough defining longitudinal axis178. A piercing tip 183 at the distal end of the cannula has an outsidediameter of at least 2 mm (0.08 inch). The piercing tip has a generallyplanar surface 184 positioned at an obtuse angle A with respect tolongitudinal axis 128.

The syringe barrel is made of thermoplastic material and tip 28 isformed in intimate contact around proximal end 73 of the cannulaengaging the annular grooves and projections so that lumen 77 is influid communication with chamber 23. Cannula 71 preferably projectsdistally from the distal wall of the barrel for a distance of at least23 mm (0.9 inch). In this preferred embodiment cannula 21 extends atleast 23 mm (0.9 inch) beyond the distal end of tip 28. Thethermoplastic material of the cannula has a higher flexural modulus thanthe thermoplastic material of the barrel. The flexural modulus of thecannula material is at least 50% higher than the flexural modulus of thebarrel material. In this embodiment, the barrel is preferably formed ofpolypropylene and the cannula is preferably made of polycarbonate.

In the prior art, short hypodermic needle assemblies and shortcannula-like spikes are used to withdraw liquid from a stoppered vial.Because these elements are removable, the syringe assembly used in theprocedure can be subsequently improperly used with a needle forinjecting substances into a person. In the case of a hypodermic needlebeing used to access the vial, the needle can also be improperly used ifnot properly disposed. The single-use syringe of the present embodimenteliminates these problems by providing an integral cannula and syringebarrel wherein the cannula has a large piercing tip not suitable forinjecting substances into people. Further, it is easier to dispose ofsince it does not have any metal components. However, an integrallyformed barrel and cannula having a short cannula would not be suitablefor drawing liquid from a glass ampoule since the ampoule cannot beinverted without spilling the liquid and the cannula must be long enoughto reach to the bottom of the ampoule. For these applications, a longhypodermic needle is used. This combination results in the same problemsas having a potentially re-usable needle assembly and syringe barrelreusable for human injection as previously described. Further, a longplastic cannula made of commonly used plastics for these applications,such as polypropylene, may bend or become damaged if it were used in anattempt to pierce a stoppered vial. This is due to the long length ofthe cannula which renders it generally undesirable for piecing vials. Itis an important aspect of the present invention that all of theabove-mentioned problems are overcome by providing a syringe assemblyhaving permanently attached cannula with a relatively large piecing tipwhich is not suitable for human injection. Further, the cannula is longenough to access vials yet strong enough to piece vial stoppers toeffectively withdraw liquid from a vial. Also, disposal is simplifiedbecause there are no metal components in the syringe assembly. The issueof strength is addressed by forming the cannula of a substantially morerigid material than the barrel. Also when the stopper is a rigidelement, as in the preferred embodiment, the barrel must be flexibleenough to provide a fluid-tight seal around the periphery of thestopper. The more rigid material used in the cannula could not be usedin the barrel because the barrel would not have the necessaryflexibility to provide an efficacious seal around the stopper and stillallow the plunger rod to move with respect to the barrel when reasonableforces are applied. The syringe assembly of the present inventionovercomes the deficiencies of the prior art by providing areconstitution syringe having a rigid plastic cannula with a tip notsuitable for human injection which can adequately access stoppered vialsand glass ampoules to reconstitute medication and subsequently to beeasily destroyed and not be a danger for drug is-use.

Single-use syringe 20 is assembled by placing locking element 51 on theplunger rod so that leg members 56 and 57 are in longitudinal slots 39and 40 and then plunger rod 31 with locking element 51 is inserted inthe proximal end of the barrel. The position of the locking element onthe plunger rod when the syringe is assembled determines the maximumdose the syringe assembly can deliver. Single-use syringe 20 asassembled and ready to use is illustrated in FIGS. 6 and 7. Deflectableresilient elements 64 and 65 on the locking element work in conjunctionwith ratchet-like teeth 43 to allow the plunger rod to move in theproximal direction with respect to the locking element to draw liquidinto the barrel as illustrated in FIGS. 8 and 9. The locking elementcannot move in a proximal direction due to the engagement of distal endbarbs 58 and 59 and proximal end barbs 62 and 63 with the inside surfaceof the barrel. However, the ratchet-like teeth working in conjunctionwith the deflectable resisting elements allow the plunger to moveproximally with respect to the locking element to fill a syringe barrel.To discharge liquid from the chamber of the barrel, force is applied tothe thumb press of the plunger rod to move the plunger rod in a distaldirection with respect to the barrel. As plunger rod 31 moves distallyin barrel 21 the interaction of the ratchet-like teeth and deflectableresilient elements on the locking element cause the locking element tomove distally in the barrel along with the plunger rod until the stoppercontacts distal wall 27 of the barrel. At this point the plunger rod canno longer move distally within the barrel and it can no longer moveproximally within the barrel because the distal end barbs 58 and 59 andthe proximal end barbs 62 and 63 are engaging the barrel and preventingwithdrawal of the plunger rod from the barrel.

Locking element 51 further includes distally directed cutting edge 67which provides further protection against improper re-use of thesingle-use syringe. By applying excessive proximally-directed force tothe plunger rod, as illustrated in FIG. 12, the stopper will be pulledproximally with respect to the cutting edge causing the cutting edge tocut through the stopper or to severely damage the stopper so that thestopper is cut and disfigured and can no longer function effectively todischarge liquid from the barrel.

The present embodiment of the single-use syringe having a thermoplasticcannula with a piercing tip can be used to reconstitute medicationswherein the liquid component is contained in a stoppered vial. Asillustrated in FIG. 14, stoppered vial 90 includes a vial 91, apierceable stopper 92, a sheet metal closure 93 for holding the stopperin place on the vial and a quantity of sterile liquid 94. The liquid isdrawn into the syringe using known clinically accepted methods whichinclude piercing the stopper of the vial with piercing tip 83 of cannula71 and moving the plunger in a proximal direction with respect to thebarrel to draw liquid into the chamber of the barrel while the vial isinverted so that the short length of cannula can access all of theliquid in the vial. The plunger can draw liquid into the barrel untildistal end barrier 46 contacts locking element 51. Syringe 20 withintegral cannula 71 is then withdrawn from the stoppered vial and usedto transfer liquid into the dried or lyophilized medication, such asvaccine, for subsequent injection into the patient. The vaccine may alsobe contained in a stoppered vial. If so, the integral cannula of thesyringe assembly can again be used to pierce the stopper and force thewater into the medication containing vial for subsequent injection intoa patient.

FIG. 15 illustrates syringe assembly 20 being used to withdraw sterileliquid from a glass ampoule 95 containing sterile liquid 94. For thisapplication, the cannula must be small enough to enter the severed neckof the ampoule and long enough to access sterile liquid 94 at the bottomof the ampoule. It is anticipated that a cannula with an effectivelength of 23 mm (0.9 inch) to 38 mm (1.5 inch) will be able to work withthe majority of ampoules believed to be available. It is preferred thatthe effective length be measured from the distal end of the barrel tipto the distal end of the cannula since it is anticipated that a barreltip of adequate strength will be much larger than the cannula and notsuitable to enter some ampoules. However, if the barrel tip is smallenough to fit into the ampoule, the effective length can be measuredfrom the distal wall of the barrel.

The flexural modulus of the cannula material, measured in units Mpa isat least 50% greater than the flexural modulus of the barrel material.Preferred materials for the barrel and the cannula are polypropylene andpolycarbonate respectively. Polycarbonate, having a flexural modulus ofabout 2275 Mpa gives the cannula the substantial strength it needs tofunction properly and still be long enough to access the full depth ofan ampoule and the polypropylene, having a flexural modulus of about1100 Mpa, provides a relatively flexible, less rigid, barrel that willprovide an adequate seal for a thermoplastic stopper made of materialsuch as polyethylene. Also, the shrinkage rate of polypropylene in themolding process is greater than the shrinkage rate of polycarbonate sothat as the molded polypropylene which surrounds the proximal end of thepolycarbonate cannula solidifies the barrel tip will shrink tightlyaround the polycarbonate needle to hold it even with more force than ifthe materials had similar shrinkage rates. Accordingly, even if thepolycarbonate cannula is still in the process of solidifying injectionmolding of the barrel over the cannula is possible.

Referring to FIGS. 17-19, the single-use syringe of the presentinvention can also be used with a removable needle assembly forreconstitution or injection and the like. Needle assembly 270 includes acannula 271 having a proximal end 273, a distal end 275 and a lumen 277therethrough, and a hub 276 having an open proximal end 279 including acavity 280 therein. A distal end 285 of the hub is joined to theproximal end of the cannula so that the lumen of the cannula is in fluidcommunication with the cavity. Tip 28 of the barrel removably engagesthe hub of the needle assembly so that the lumen is in fluidcommunication with the barrel chamber. The distal tip of the cannula maybe a stopper piercing tip as described hereinabove or a sharp bevel tipsuitable for injection such as tip 283.

Referring to FIG. 20, the single-use syringe of the present inventioncan also be used with a permanently attached cannula 371 having aproximal end 373, a distal end 375 and a lumen therethrough. Barrel 321includes a tip 328 with a passageway 329 therethrough. The proximal endof the cannula is positioned in the passageway and held permanently tothe barrel tip through the use of adhesive 330. There are numerous waysto permanently attach a cannula to a barrel tip such as a press-fit,crimping the barrel tip, and the like, all of which are within thepurview of the present invention with the adhesive connectionillustrated being merely representative of these many possibilities. Thedistal tip of the cannula may be a stopper piercing tip as describedhereinabove or a sharp bevel tip suitable for injection such as tip 383as illustrated in FIG. 20.

1. An operable single-use syringe comprising: a barrel having an insidesurface defining a chamber for retaining fluid, an open proximal end anda distal end having a distal wall with a tip extending distallytherefrom having a passageway therethrough in fluid communication withsaid chamber; a plunger rod including an elongate body portion defininga longitudinal axis, a proximal end and a distal end, a stopper at saiddistal end slidably positioned in fluid-tight engagement in said barrel,said body portion extending outwardly from said open proximal end ofsaid barrel, said body portion including two parallel longitudinalslots, at least one of said slots including a plurality of axiallyspaced discontinuities; a locking element positioned in said barrelbetween said elongate body portion of said plunger rod and said insidesurface of said barrel, said locking element having a proximal end, adistal end, a base and two leg members in substantially parallelrelationship extending from said base into each of said longitudinalslots, said locking element having an outwardly and distally directeddistal end barb and an outwardly and distally directed proximal end barbfor engaging said inside surface of said barrel to prevent proximalmotion of said locking element with respect to said barrel, said legsincluding at least one deflectable resisting element for engaging saiddiscontinuities on said plunger rod for moving said locking element in adistal direction along said inside surface when said plunger rod isadvanced in a distal direction and allowing proximal motion of saidplunger rod with respect to said locking element for filling saidchamber.
 2. The single-use syringe of claim 1 wherein locking elementincludes a second outwardly and distally directed distal end barb. 3.The single-use syringe of claim 1 wherein said locking element includesa second outwardly and distally directed proximal end barb.
 4. Thesingle-use syringe of claim 1 further including a proximal end barrierat said proximal end of said body portion of said plunger rod forestablishing the most proximal position of said locking element on saidplunger rod.
 5. The single-use syringe of claim 4 wherein said proximalend barrier blocks access to said locking element through said openproximal end of said barrel.
 6. The single-use syringe of claim 4further including a distal end barrier at said distal end of said bodyportion of said plunger rod establishing the distal-most position ofsaid locking element on said plunger rod.
 7. The single-use syringe ofclaim 1 wherein said at least one deflectable proximal resisting elementincludes a deflectable resisting element on each leg member.
 8. Thesingle-use syringe of claim 7 wherein each of said longitudinal slotsincludes a plurality of axially spaced discontinuities.
 9. Thesingle-use syringe of claim 8 wherein said deflectable resistingelements face outwardly away from each other and said plurality ofaxially spaced discontinuities in each slot face inwardly toward eachother.
 10. The single-use syringe of claim 6 wherein the axial length ofsaid locking element is less than 20% of the distance between saidproximal end barrier and said distal end barrier.
 11. The single-usesyringe of claim 1 wherein said locking element includes a distallydirected cutting edge at its distal end capable of cutting into saidstopper if excessive proximally-directed force is applied to saidplunger rod to overcome said locking element and remove said plunger rodfrom said barrel.
 12. The single-use syringe of claim 1 wherein saidplunger rod and said stopper are integrally formed of the same material.13. The single-use syringe of claim 1 wherein said locking element ismade of sheet metal.
 14. The single-use syringe of claim 1 furthercomprising a needle assembly including a cannula having a proximal end,a distal end and a lumen therethrough, a hub having an open proximal endincluding a cavity therein, a distal end joined to said proximal end ofsaid cannula so that said lumen is in fluid communication with saidcavity, said tip of said barrel engaging said hub so that said lumen isin fluid communication with said chamber.
 15. The single-use syringe ofclaim 1 further comprising a cannula having a proximal end, a distal endand a lumen therethrough wherein said proximal end of said cannula isconnected to said tip of said barrel so that said lumen is in fluidcommunication with said passageway.
 16. The single-use syringe of claim1 further comprising: an elongate cannula made of thermoplasticmaterial, said cannula having an outside surface, a proximal end, adistal end and a lumen therethrough defining a longitudinal axis, saidoutside surface at said proximal end including at least onediscontinuity, said distal end having a stopper piercing tip; and saidbarrel being made of thermoplastic material, said tip of said barrelbeing formed in intimate contact around said proximal end of saidcannula engaging said at least one discontinuity so that said lumen isin fluid communication with said chamber, said cannula projectingdistally from said distal wall.
 17. The single-use syringe of claim 16wherein said tip of said cannula includes a closed distal end and atleast one side aperture in fluid communication with said lumen.
 18. Thesingle-use syringe of claim 16 wherein said tip of said cannula includesa planar surface and at an angle with respect to said longitudinal axis.19. The single-use syringe of claim 16 wherein said cannula projectsdistally from said distal wall of said barrel for a distance of at least23 mm (0.9 inch).
 20. The single-use syringe of claim 16 wherein thedistal end of said cannula has an outside diameter of at least 2 mm(0.08 inch).
 21. The single-use syringe of claim 16 wherein saidproximal end of said cannula has an outside diameter of at least 2.5 mm(0.1 inch).
 22. The single-use syringe of claim 16 wherein saidthermoplastic material of said cannula has a flexural modulus of atleast 50% greater than the flexural modulus of said thermoplasticmaterial of said barrel.
 23. The single-use syringe of claim 16 whereinsaid cannula is made of polycarbonate.
 24. The syringe assembly of claim16 wherein said barrel is made of polypropylene.
 25. An operablesingle-use syringe comprising: an elongate cannula made of thermoplasticmaterial, said cannula having an outside surface, a proximal end, adistal end and a lumen therethrough defining a longitudinal axis, saidoutside surface at said proximal end including at least onediscontinuity, said distal end having a stopper piercing tip; athermoplastic barrel having an inside surface defining a chamber forretaining fluid, an open proximal end and a distal end having a distalwall with a tip extending distally therefrom having a passagewaytherethrough in fluid communication with said chamber, said tip beingformed in intimate contact around the proximal end of said cannulaengaging said at least one discontinuity so that said lumen is in fluidcommunication with said chamber, said cannula projecting distally fromsaid distal wall for a distance of at least 23 mm (0.9 inch), saidthermoplastic material of said cannula having a higher flexural modulusthan said thermoplastic material of said barrel; a plunger rod includingan elongate body portion defining a longitudinal axis, a proximal endand a distal end, a stopper at said distal end slidably positioned influid-tight engagement in said barrel, said body portion extendingoutwardly from said open proximal end of said barrel, said body portionincluding two parallel longitudinal slots, each of said slots includinga plurality of axially spaced discontinuities; and a locking elementpositioned in said barrel between said elongate body portion of saidplunger rod and said inside surface of said barrel, said locking elementhaving a proximal end, a distal end, a base and two leg members insubstantially parallel relationship extending from said base into eachof said longitudinal slots, said locking element having two outwardlyand distally directed distal end barbs and two outwardly and distallydirected proximal end barbs for engaging said inside surface of saidbarrel to prevent proximal motion of said locking element with respectto said barrel, said legs each including a deflectable proximalresisting element for engaging said discontinuities on said longitudinalslots for moving said locking element in a distal direction along saidinside surface when said plunger rod is advanced in a distal directionand allowing proximal motion of said plunger rod with respect to saidlocking element for drawing fluid into said chamber.
 26. A single-usesyringe of claim 25 wherein further including a proximal end barrier atsaid proximal end of said body portion of said plunger rod establishingthe most proximal position of said locking element on said plunger rod.27. The single-use syringe of claim 26 wherein said proximal end barrierblocks access to said locking element through said open proximal end ofsaid barrel.
 28. The single-use syringe of claim 25 further including adistal end barrier at said distal end of said body portion of saidplunger rod establishing the distal-most position of said lockingelement on said plunger rod.
 29. The single-use syringe of claim 25wherein said locking element includes a distally directed cutting edgeat its distal end capable of cutting into said stopper if excessiveforce is applied to said plunger rod to overcome said locking elementand remove said plunger rod from said barrel.
 30. The single-use syringeof claim 25 wherein said thermoplastic material of said cannula has aflexural modulus of at least 50% greater than the flexural modulus ofsaid thermoplastic material of said barrel.
 31. The single-use syringeof claim 25 wherein said plunger rod and said stopper are integrallyformed of the same material.
 32. The single-use syringe of claim 25wherein said locking element is made of sheet metal.
 33. The single-usesyringe of claim 25 wherein the cannula is made of polycarbonate.